The present invention relates to an apparatus and method for forming films and, more particularly, to an apparatus and method for forming a thin film (with film thickness 100 .mu.m or less in wider sense, 10 .mu.m or less in general) on a substrate or the like by discharging a solution-state substance through micro-nozzles. The invention can be applied, for example, to thin film formation processes suited to the fabrication of hybrid IC circuits, semiconductor circuits, or micromachines.
In recent years, the thin film formation technique has been applied to a variety of fields. The actual system for film formation has also been discussed over a wide range including spin coating, printing, and die coating, other than those which need vacuum equipment such as sputtering and deposition systems.
Among these, in particular, the spin coating system is often used for the resist coating, protective film formation, and the like in semiconductor processes.
Here is an explanation of a conventional spin coater.
FIGS. 20A, 20B, and 20C illustrate the construction and operation of a common conventional spin coater.
In FIGS. 20A, 20B, and 20C, there are shown a spindle 101 of the spin coater, a sample fixing base 102, a nozzle 103 for discharging coating liquid, a substrate 104 on which a thin film is to be formed, liquid 105 and 106, a thin film 107, and spattered droplets 108.
With such an arrangement, as shown in FIG. 20A, the liquid 105 is first discharged from the nozzle 103 toward the substrate 104 so as to be placed on the substrate 104.
Next, as shown in FIG. 20B, the spin coater is rotated at a low speed .omega..sub.1, so that the liquid 106 is spread on the substrate 104.
Then, as shown in FIG. 20C, the spin coater is further rotated at a higher speed .omega..sub.2, so that the thin film 107 is formed on the substrate 104.
However, with the above conventional arrangement, there would occur spattered droplets 108 that are dissipated in vain, as shown in FIG. 20C, such that 80 to 90% of the liquid would be discarded.
The reason of this is that the substrate 104 would be left partly uncoated at portions of poor compatibility with the liquid 105 unless the liquid 105 is discharged in large amounts.
As seen above, the conventional spin coater is poor at use efficiency of the liquid, and has had an issue that most of the coating liquid would be wasted.
Also, when a spin coater is used to form a film, the liquid flows from inside toward the outer periphery so that the outer peripheral portion becomes large in film thickness. This would causes distortion of the disk itself.
On the other hand, conventionally, as printing equipment, there have been energetically developed liquid dispensers using a micro-nozzle to discharge ink. As an application of such liquid dispensers, there have been developed in recent years liquid dispensers or circuit forming methods which use solutions other than ink, for example, resist, as the solution to be discharged, with a view to applying them to the fabrication of IC circuits and the like.
Now the prior art is described below by taking the liquid substance coating device of Japanese Laid-Open Patent Publication No. 5-104052 as an example.
FIG. 21 shows the construction as disclosed in Japanese Laid-Open Patent Publication No. 5-104052.
In FIG. 21, there are shown a liquid substance feed part 201, a discharge head 202 connected to the liquid substance feed part 201, a member to be coated 203 (hereinafter, referred to as substrate), an X-Y stage 204 for positioning the discharge head 202 and the substrate 203 so that they are opposed to each other.
The discharge head 202 comprises a pressure chamber 206 which communicates with the liquid substance feed part 201 and into which a liquid substance 205 is filled, a nozzle 207 provided at a longitudinally intermediate point of the pressure chamber 206 and opened to a lower end face of the discharge head 202, a displacement amplifying chamber 209 to which a displacement is given by a piezoelectric device 208 and which amplifies the displacement, and a diaphragm 210 provided at the boundary between the pressure chamber 206 and the displacement amplifying chamber 209.
Then, the piezoelectric device 208 is driven by a control part 211, and a displacement thereby generated is transferred through the displacement amplifying chamber 209 and the diaphragm 210 to the liquid substance 205 within the pressure chamber 206. As a result, the liquid substance 205 within the pressure chamber 206 is pressurized, so that the liquid substance 205 is spattered downward from the nozzle 207 in the form of liquid droplets 205a.
Adopting such a constitution makes it possible to spatter the liquid substance 205 contained in the nozzle 207 onto the substrate 203 in the form of liquid droplets 205a, and thereby to apply the liquid substance 205 on the substrate 203 in any given pattern.
It is noted that the X-Y stage 204 is controlled to a desired position by the control part 211.
Meanwhile, in the above-described conventional constitution, since the piezoelectric effect is primarily utilized as the method of discharge, there are some issues to be overcome as described below.
In the discharge method of the pressure-applying system using the piezoelectric effect (hereinafter, referred to as piezoelectric system), the solution to be discharged is formed into discharge droplets having diameters two to three times larger than the nozzle diameter. This poses restrictions on the miniaturization and precision of circuit patterns to be formed by the discharge liquid.
Next, in order to enhance the miniaturization and precision of circuit patterns, it is necessary to reduce the nozzle diameter. However, the more the nozzle diameter is reduced, the larger adhesion loss at the nozzle portion the piezoelectric system discharge method involves. Thus, there are limitations in reducing the nozzle diameter, especially in the case of high viscosity solutions.
Further, in the piezoelectric system discharge method, if some organic solution with a large amount of dissolved air is used as the discharge solution, there would occur the cavitation phenomenon, resulting in unstable discharge. Therefore, the kinds of solutions that can be discharged would be limited to a small extent.